1. Field of the Invention
The present invention relates to an automobile seat capable of preventing a seat occupant from suffering a whiplash injury when an automotive vehicle has come into a rear-end-collision.
2. Description of the Related Art
Automobile seats generally have a headrest mounted on an upper portion of a seat back. When a user sits on a seat, a predetermined clearance is present between a user's head and the headrest, but when an automotive vehicle has come into a rear-end-collision, a user's body moves rearward, and the user's head moves further rearward. Accordingly, a load is applied to a user's neck, thus resulting in a whiplash injury.
It is possible to reduce the clearance between the user's head and the headrest to minimize the injury. In this case, however, the user's head is often brought into contact with the headrest even in a normal sitting condition, and even a slight movement of the head causes the head to interfere with the headrest, thus making the user uncomfortable.
A headrest mounting structure for an automobile seat has been proposed in which a seat back frame is made up of an upper frame and a lower frame connected to each other via a hinge, and a headrest is mounted on an upper portion of the upper frame. In this headrest mounting structure, an impact plate is provided at a lower portion of the upper frame so as to confront a seat occupant's back, and a coil spring is also provided to bias the impact plate forward and the headrest rearward.
If an impact is applied to a rear portion of an automotive vehicle, the impact plate is moved rearward by a rearward movement of the seat occupant's body, followed by a forward movement of the headrest, which in turn supports the seat occupant's head (see, for example, Patent Document 1).
Document 1: Japanese Laid-Open Patent Publication No. 10-119619
In the case of the headrest mounting structure as disclosed in Document 1, however, the headrest and the seat back tend to return to initial positions thereof by a biasing force of the coil spring after the forward movement of the headrest and, hence, the support of the seat occupant's head becomes insufficient, thus giving rise to a problem that a strain on a cervical vertebra cannot be sufficiently reduced.